The Four: Honda’s Iconic 750

Great motorcycles are almost always defined by their motors, and Honda’s original 1969 CB750K0 is no exception. Known simply as the K-Zero to insiders, the Honda was the first mass-produced four-cylinder in the motorcycle world that was widely available. In an era of twins, its cylinder count alone doubled the ante. And it was a cannon-shot across the bow of every other motorcycle company in the world.

The formula was simple and outrageous at the same time: Four cylinders set in a transverse configuration across the frame. Air-cooled. The single overhead cam was a real improvement in an era that still used pushrods, and helped raise the K0’s redline and output: 8500 rpm produced 68 horsepower. Top speed was 125 miles per hour. The engine and transmission were built as a single unit (again, the rule today but not the formula followed by other big-bike builders of the time). Four carburetors fed the engine, and an electric starter took all the drama out of getting underway.

Step back 40 years, and three things strike you about the K0 engine: First, it makes a huge statement—wide, with four cylinders and four pipes, a complete exaggeration of what you expect a motorcycle engine to be. Second, the design is super clean: no external oil lines clutter the exterior. The pipe-carburetor-fin theme just keeps repeating from side to side, an exercise in elegant symmetry. You can’t see any primary drive, and the gearbox is part of the engine case. And third, the engine puts out its bountiful power in a, for the time, endless, smooth curve. Twins of the day shook so badly they fractured mounting lugs, but the Honda Four was as smooth as a turbine.

Honda built its first-generation CB750s from 1969 until 1978. Its advantages were so obvious that it completely redefined what a motorcycle should be, and indeed, even four decades later, Honda’s CBR1000RR and CBR600RR use fundamentally the same architecture, albeit now with liquid cooling, twin cams and more valves. Proof, if there ever was, just how far ahead that first engine saw into the future.